I would really love an update on this, too. Where is it in terms of priority? Is it on the radar at all? Patch 2 is out now and...nothing. My main game is on hold in hopes that a fix will still allow this quest to trigger.
For information purposes, I WAS able to get this quest to trigger in my second game by doing the following:
-recruit Dorian
-immediately obtain Skyhold
-immediately talk to Dorian upon regaining control. At second initiation of conversation (I didn't leave, I just exited the conversation then initiated it again), the scene with Felix's letter triggered, which in turn triggered Mother Giselle moving to the throne room to give me Last Resort of Good Men, and everything proceeded as normal.
The difference between my broken game and my second game is mostly how much I quested with Dorian PRIOR to Skyhold. In my broken game, I did every available quest he had, war table and otherwise. I racked up tons of approval for him.
In the second game I avoided any questing and went right to Skyhold after recruiting him, and his personal quest triggered successfully. I DID exhaust all conversation with him at Haven, and Skyhold was NOT cleaned up or updated at all, and the quest still triggered. Seems largely to hinge on how much approval you have with him prior to Skyhold?
Anyway, that at least let me see the quest, but I'd still reeeeally appreciate a fix for this. It sucks to take Dorian from new acquaintance right to bestie/romance with no time in between. Really screws up the pace of the story.